Protos Armored Car is rather "new", because first info about it was published in 2011: http://armoredcars-ww-one.blogspot.com/2011/12/mexican-fiat-armored-car-federal-army.html The author of this blog (Jose Luis Castillo) informed us that it was a German armored car sold to Mexico.

Later, in 2013, Rainer Strasheim in his "Panzer-Kraftwagen..." wrote that this car was used by Germans on the Eastern Front in 1914 and captured by Russians! As a proof he published two photos from some Russian newspaper (photos courtesy of Stanislav Kiriletz).

In 2015 Jose Luis Castillo again wrote about Protos: http://armoredcars-ww-one.blogspot.com/2015/01/panzerauto-protos-german-armored-car.html and he repeated info that it was sold to Mexico and that only one was built.

So either there were at least two Protos armored cars or the story of Protos on the Eastern Front is a mistake. With all due respect, because all these guys (Strasheim, Kiriletz and Castillo) are experts and I love their writing.

I don't think there is any other source of information about this mysterious and fascinating vehicle.